Depends on how intense the applications are that you are running. When I'm using mine for normal daily activities like mail, iTunes, Safari, and Office Suite, I never use any 3rd party fan apps. When I use it for gaming or video compression I increase the fans mainly because it is easier to replace a failed fan than a failed CPU or GPU in rMBP. I don't think its necessary to run any 3rd party apps, but for the reason I stated in the last sentence.
Was doing some major iPhoto library surgery yesterday, splitting 70GB into separate album archives for each year, and it got surprisingly hot when deleting thousands of pictures (within iPhoto). At 100°C the fans finally revved up, but still barely a whisper. I immediately overrode the defaults and went full speed, eventually dropping temps back to about 70°C during deletes.
This was totally unexpected; CPU graph didn't show significant activity, and duplicating the master archive each time didn't raise the temps either. This suggests the GPU was in play, the only other time I've had such temperature spikes was playing games. No idea why the GPU might be used for deleting photos (re-generating thumbnails, I'd understand).